A brake system of the aforementioned type has been described, for example, in DE OS 38 31 426.
The pump has the function to deliver the pressure fluid discharged during a control from the wheel brakes back into the brake conduit. For that purpose, the intake side of the pump is in communication with a pressure fluid collector capable of being connected to the wheel brakes, while the pressure side of the pump is in communication with the master brake cylinder. The pump, hence, is connected in shunt with the brake conduit so that no pressure fluid flows therethrough during pedal operated braking.
A connection of the intake side to the master brake cylinder is established only during a traction slip control. In that case, the pump will suck off pressure fluid from the reservoir associated to the master brake cylinder, delivering the same to the wheel brake. However, this will occur only in the inoperative condition of the master brake cylinder, i.e., in a non-pressurized condition.
A circuit of the afore-described type involves two essential disadvantages. In brake slip control, the pump delivers from the non-pressurized pressure fluid collector against the pressure in the master cylinder with the consequence that especially with a cold and viscous brake fluid, the full power of the pump will be reached only after an extended start-up phase which, in turn, will result in a deteriorated control quality.
Another disadvantage resides in that the automatic suction pump forms vacuum if no adequate pressure fluid is available on the intake side thereof. Air is liable to flow into the vacuum if damage is done to the corresponding seals. It is difficult to remove such air from the brake system as the pump is in shunt with the brake conduit, with air voids in the brake system being likely to result in a failure of the brake system.
It is, therefore, the problem of the invention to provide a hydraulic brake system which irrespective of the ambient temperature, permanently insures a high control quality and exhibits a low failure probability, thus permitting a particularly easy ventilation.